i don't know how to make it constructive other than saying they simply look bad
but one thing (especially noticable on the tram/rocketL) is that they just look poorly constructed. You can see the little lines where it looks like instead of welding you've just jammed shapes as close as possible to get it right. i might be wrong, but if you post the ms3d or blend files or whatever you use i can show you what i mean